Manufacture of pulp and paper from resinous woods



' Patented Nov. 3, 1931 UNITED STATES PATENT 1 ounce LI N BRADLEY, or MoNrcLArR, NEW JERSEY, AND EDWARD r. MOKEEFE, or PIiATTS- uRo, NEW YORK, ASSIGNORS ro BRADLEY-MCKEEFE CORPORATION, on; NEW YoRx, N. A CORPORATION on NEW YORK MANUFACTURE OF PULP AND PAPER FROM RESIKOUS WOODS No Drawing.

ferior value for the production of high-grade pulp and paper, and especially for the production of commercially bleachable pulp.

In our prior application, Serial No. 481,147,

filed June 28, 1921, among other disclosures we have described the production of pulp from resinous'woods by subjecting the wood to cooking operation with a cookmg llquor containing essentially a normal alkali sulfite to which sometimes a small amount of caustic alkali was added to assist in removing the resinous constituents, while in other cases caustic alkali was added in small amount duringthe latter stage of the cook.

The present invention relates to an improved method of cooking such coniferous Woods with a solution containing sodium sulfite as an active ingredient, and more particularly to the cooking of such woods with such a cooking liquor wlthout the use of caustic soda. According to the process of the present invention, cooking of these woods can be conducted in a simple manner with the production of a satisfactory yield of good quality chemical pulp and with little if any uncoo ed chips or screenings.

In our investigations, which have included commercial operations on large mill scale, we have found that coniferous woods, and especially those which contain an appreciable amount of resinous constituents, are more difficult to treat with a sodium sulfite cooking liquor than the ordinary non-coniferous woods, and that certain operating difiiculties were presented in the cooking of such coniferous and resinous woods which were not presented in the cooking of ordinary nonconiferous deciduous woods. For example, in cooking poplar (Populus grandz'dentata) wood chips with a solution which contained 30% or more of normal sodium sulphite, based on the bone dry wood, the cooking liquor being a 10% solution of Na SO we Application filed May a, 1924. Serial No. 711,857.-

that after such obtained splendid results both as to yield and quallty of the pulp, by bringing the temperature up to about 183 C. in a short time, which may be one half an hour or so, and holding at this temperature for four hours. When we endeavored to cook air dry spruce and balsam wood chips by following a similar,

procedure, including rapid heating, the resulting pulp was of an inferior quality and contained a large percentage of underdone chips, which generally had fibrous ends but with hard centers which were of brown color. We then endeavored to recook these chips with the hard, brown centers, in an additional amount of sodium sulphite cooking liquor, but the results were quite unsatisfactory. However, these underdone chips can be readilypulped by cooking with a cooking liquor whlch contains a small amount of caustic soda, as described in our said earlier application, or the caustic soda may be added to the digester charge toward the end of the cookin operation, care being takento carethe cooking liquor, and these chips can then be readily pulped.

In our investigations, we spruce, pine and balsam chips to a preliminarytreatment with a dilute solution of J caustic soda or of sodium carbonate, especially at temperatures above 100 C., in order to remove some of the resinous constituents, and facilitate. the production of suitable yields and quality of chemical pulp .by using a cooking liquor which contained the necessary I amount of sodium sulphite, without using any additional caustic soda, either with the cooking liquor in the original charge or added toward the end of the cook or even after the sodium sulphite cooking operation had beenconcluded; but "our investlgations indicated reliminary treatment with caustic soda or sodium'carbonate, these treated chips were even more diflicult to pulp in a satisfactory manner, and the conclusion was Y reached that the chips had been so acted on or changed chemically as to inhibit the reaction by which the sodium sulphite renders soluble the non-fibrous constituents of the. wood.

were cooked with water at temperatures much 7 above 100 0., the chips were so changed that contained essentially sodium sulphite.

We have found, however, that if the 1mtreated coniferous or resinous wood chips are subjected to a preliminary impregnation with the sodium sulphite cooking liquor, and the chips thoroughly penetrated and impregnated with theliquor before the digester 1s brought to a high temperature, the digester charge can then be heated to the necessary high temperature for the cooking operation, and the entire digester charge can-be cooked in a satisfactory manner and with substantial avoidance of screenings or uncooked portions of the chips, with a cooking liquor which contains essentially sodium sulphite, and without the addition of caustic soda thereto.

We have found, for example, in our investigations, that when the untreated coniferous wood chips were soaked for several hours in a solution of sodium sulphite free from caustic soda and sodium carbonate, at ordinary temperature, and quite thoroughly ing operation so as to produce a satisfactory yield and quality of chemical pulp. it became diflicult to convert them into satisfactory pulp by cooking with a solution which I Our investigation of the chemical reactions which take place during the cooking of woods for the production of pulp lead us to consider that wood is a complex chemical substance made up of different constituents, which react differently with different chemicals and under different conditions of operation. Wood appears to contain in its non-fibrous portion certain organic compounds which are of ketonic or aldehydic character when in its ordinary condition as received at the pulp mill. These particular constituents appear to have the peculiar property of being converted into Water soluble compounds when they are combined in some manner with the sulphite radical. They appear also to be of such character that they may be quite readily decomposed or changed iIlKO compounds having different properties by treatmentw'ith steam or water at temperatures much in excess of 100 C., and apparently may also be changed into other compounds by treatment with caustic soda, sodium carbonate, sodium sulphide, and other active reagents, especially at tempera im regnated with the solution in the digester/tures in excess of 100 C. We do not wish to be ore the digester cover was put on, and by then heating the digester slowly and gradually by external means, the digester charge could be finally cooked for several hours at a temperature above that corresponding to 100 lbs. steam pressure, and uniformly treated chips produced, forming a pulp free from shives and uncooked chips, and a pulp which was entirely satisfactory.

As a result of our investigations, carried out upon various lots of coniferous wood chips, we have found in general that the rapid raising of the temperature of the cooking liquor to the maximum without proper preliminary treatment of the chips, gave unsatisfactory results. But we have found that where the temperature was raised slowly and gradually so that the liquor penetrated the chips to an adequate degree before the temperature reached the critical point at which the change apparently occurs which is re ferred to above, coniferous wood chips, and especially even those which contain appreciable amounts of resinous constituents, may be satisfactorily pulped by a cooking'liquor which contains the necessary amount of sodium sulphite, and without the use of caustic soda or sodium carbonate. We have found the observance of proper conditions for limit ourselves by any theoretical explanation of the complex chemical reactions which take place whenwood is cooked with r; solution of normal sodium sulphite, but we are led to believe that it is because of some re- In carrying out the process,of the present" invention we avoid the too rapid raising of.

raise the temperature of the charge gradually and slowly to the cooking temperature. In general, we aim to give to eachand every chip of wood the same or nearly the same treatment as regards the"quantity of sodium sulphite per unit of non-fibrous material to be rendered soluble and to subject all the wood chips to cooking liquor of the same or nearly the same concentration and composition'and to the same or nearly the same temperature conditions for approximately the same length of time. Where, however,the charge of wood chips contains chips which differ somewhat as to penetrability, or as to some other factor,

the cooking conditions are regulated so that' nearly all of the chips which are the more difficult to pulp will nevertheless be sufliciently penetrated and subjected to the chem- .pulped chips can nevertheless be adequately pulped.

We have found it advantageous, in cooking a di ester charge with the sodium sulphite coo ing liquor, 1o gradually. and slowly raise the temperature so as to insure adequate penetration of the wood chips, especially those chips which are the more diflicult to penetrate, with the cooking liquor before the critical temperature is reached, so that these chips are not objectionably changed during the cooking operation, but are adequately cooked instead. We have found this adual and slow raising of temperature .to e par-- ticularly important and advantageous With a normal sodium sulphite cookin liquor which does not contain any appreciable amount/of caustic soda or other reactive compounds, and where the wood chips cooked are coniferous woods containing appreciable amounts of resinous constituents. i

large territory, especially in the northern Lake States of the United States and in Can'- ada east of the Province of Saskatchewan. Similar pines are abundant in regions west of the aboveterritory. This .jack pine generally has much darker colored wood in the center of'the log and for some distance toward the circumference, while the remainder of the log has a lighter colored wood. These two portions appear to possess somewhat different physical characteristics. The lighter colored portion appears to be more easily penetrated with the cooking liquor than the darker wood. This physical difference may explain the difiiculty which others have experienced in their efforts to obtain uniform -chemical pulp of high quality when cooking jack pine, using the sulfide radical. By the process of the present invention, however, it is quite easy to obtain good yields of excellent chemical pulp from jack pine, such pulp being accompanied by very little if any screenings or uncooked chips.

In treating coniferous woods, especiallythe kinds referred to, it will be found that the different woods differ from each other, 7

Where the cooking vessel is the usual type land that different logs of the same wood may of vertical, stationary digester, care should be taken to secure adequate circulation of the cooking liquor so that all of the chips receive approximately the same treatment during the cooking operation. Pumps and circulating v pipe lines, if employed, should be so arranged and operated as to secure substantially equal temperature and liquor composition throughout the entire mass of chips during practically all of the time the digester contents are under treatment. In rotating types of digest-ers, practically uniform treatment may be obtained without the use of pumps and circulating lines.

, The present invention relates particularly to the treatment 'of coniferous woods, and especially coniferous woods which. contain appreciable amounts of resinous constituents, and'which are commonly referred to as resinous woods. Among such woods may be mentioned the following: tamarack, larches. pines, (jack pine, Norway pine, loblolly pine, Oldfield pine, short leaf pine, long leaf pine, lodgepole pine, sugar pine, pitch pine, slash pine. scrub pine, white pine, etc.) etc.

When any of these woods are given a preliminary treatment with solvents in order to,

5 remove any of the nonfibrous constitutents,

care should be taken to avoid objectionably altering the remaining nonfibrous constituents so as to render them difficult to react with the sodium sulphite cooking liquor to produce soluble compound-s.

The process of the invention is of particular value in the production of high grade chemi-v cal pulp from the pine which is often called jack plne (Pin/us dz'oavtoata or banksiao'uz) also difier; and that various factors should be glven consideration, among them being:

the kind of wood,'the age of the wood, the

In order to secure uniform cooking conditions, it is important to use chips of uniform size and length, and chips which do not vary too greatly from each other in factors such as those above mentioned which affect I the penetration by the cooking liquor and its reaction durin the cooking operation.

The amount 0? normal sodium sulphite used in the cooking of the coniferous woods, according to the present invention, can'be somewhat varied. It is not necessary to use the minimum amount of sodium sulphite which will satisfactorily cook the wood, for we have found that a considerable amount in excess thereof can be used, and may be even advantageous, without interfering with the production 10f satisfactory pulp and without objectionable overcooking of the charge. In general, around 35% to 50% or more of sodium sulph'ite based on the bone dry weight of the wood can be satisfactorily used.

In carrying out the present process, unlined digesters of iron or steel are well adapted'for use, as the cooking liquor employed does not react in any objectionable way with these materials but remains alkaline t0 litmus which grows quite rapidly throughout a very iao necessary to provide the digesters with an acid-resisting lining, such as is now commonly provided in digesters used in the so-called sulphite process, although digesters containing such lining may be used.

The digester used in carrying out the process can be provided with thermometers at various points to indicate the temperature at various parts of the digester and in the circulating lines etc., as well as sampling devices and the like.

In carrying out the process in such digesters, we have found it advantageous to carry out the cooking opera-.ion in what may be considered two successive stages, using the cooking liquor containing normal sodium sulphite without any appreciable amount of caustic soda, sodium carbonate, sodium sulphide, etc. During the first period the digester charge is gradually heated and the temperature of the cooking liquor is slowly raised, until substantially all of the chips have been penetrated or impregnated by the cooking liquor at a temperature which does not exceed for example about 100 C. Thereafter the charge can be heated to a much higher temperature for the main cooking operation. By proceeding in this way the entire process can be carried out in the digester and the main cooking operation can advantageously be carried out at a high temperatureand pressure, considerably higher than is commonly used in the present day pulp-making operations. The useof such higher temperatures and pressures is a characteristic advantage which the present invention presents. Temperatures corresponding to as high as 140. to 180 lbs. saturated steam pressure can advantageously be used inthe process of the present invention, although somewhat lower temperatures and pressures can be satisfactorily used.

In carrying out the process it is important as above stated, to circulate the cooking liquor or otherwise to bring-it into contact with all of the chips so that a sufiicient amount of the cooking liquor will be present for the cooking of all of the individual chips and so that the cooking liquor has an opportunity of cooking all portions of the chips.

According to one method of carrying out the invention, the chips are preliminarily impregnate'd with the cooking liquor, using a liquor of sufficient concentration and quantity so that the necessary amounts of sodium sulfite for the complete cooking operation will be absorbed by the chips during this pre-' liminary impregnation. This preliminary treatment, moreover, is carried out at a temperature belowthe critical reacting point. The preliminary impregnation may be carried out either within the digester or within some other suitable container. For example, suitable chips, depending upon the nature and. condition of the wood and the product to be produced, are placed within the impregnatlng vessel, the vessel exhausted by suction as far as feasible, after which the valve connecting the vessel to the exhausting means is closed and then the valve leading to the liquor storage tank is opened, so that the difference in pressure will cause the concentrated solution of sodium sulphite to flow into the impregnating vessel and to penetrate the chips. In general, the less the amount of water remaining within the chips prior to exhaustion, the greater the amount of sulphite liquor which can be caused to penetrate the chips and be retained therein. With moderately dried chips and with a sufliciently concentrated solution of sodium sulphite, enough chemical can be retained in the chips to complete the cooking operation. The impregnating solution may be heated and may been used as the impregnating vessel, the

excess and unabsorbed liquor can be drained from the chips and returned to the liquor storage tank, prior to transferring the impregnated chips to a digester; but this liquor should not be removed until suflicient time has elapsed to produce the desired thorough (and uniform) impregnation.

In case the preliminary impregnation or treatment is carried on within a stationary vertical digester, the excess and unabsorbed impregnating liquor is removed from the digester,-e. g., by forcing it out by means of steam fed into the digester at the top, and the liquor is then run into the liquor storage tank. However, in either case a sufficient quantity of liquor should be allowed to remain in the' digester, or should be subsequently added so as to permit suitable circu-' lation of the liquor and heating of the chips within the digester as nearly as possible in a uniform manner, and to insure that all of the chips are sufficiently heated and have sufficient chemical for the cooking operation; but the amount of this circulating liquor can'be much smaller than is required for submerg- By thus reducing the volume of liquor wlthin the digester, less steam is reing the chips.

quired for heating the digester contents up to the desired temperature, and the concentration of sulfite in the solution is kept high.

' what increased to insure that suflicient of the sodium sulfite is absorbed by the chips during the preliminary impregnation. In case the chips have not retained an adequate amount of the sodium sulfite the deficiency may be made-up by using a larger amount of chemical and circulating the liquor and by heating up the digester charge in successive stages so that during the first stage the thorough penetration is brought about.

The length of time for completing the cooking operation depends upon the temperature employed, and to some extent upon the concentration of the cooking liquor, and the time elapsed in bringing the charge up to the cooking temperature, as well as the nature and condition of the resinous wood cooked.

With resinous woods, we have found it particularly advantageous to charge the chips into the digester and to charge the digester with the sodium sul hite/ cooking liquor sufficient for the cooking of the d gester charge, and then to subject the-d1- gester-charge to a preliminary heat1ng operation at a temperature below the critical temerature of reaction for a sufficient time to insure-that the chips are thoroughly treated with the liquor and with the sodium sulphite thereof, before the digester charge is later heated to the active cooking temperature. After the proper impregnation has been accomplished in the digester the temperature of the digester charge may then be raised higher and the digestion then carried to completion.

One advantageous method of charging the digester and of effecting the preliminary impregnation is to partially charge the digester with the wood chips and then add the cooking liquor and heat the cooking liquor gradually to a temperature of about 100 C. and charging additional wood chips duringthe gradual heating period referred to.

Where resinous woods are used, they can advantageously be subjected to a preliminary extraction, prior to the cooking operation, for

the extraetlon of turpentine, resins, etc., foruse as naval stores, and this preliminary extraction can advantageously be carried out at an elevated temperature; but in general it should be regulated and controlled so that the wood is not objectionably changed and effective cooking prevented. Where the wood is subjected to extraction with steam at hi h temperatures, there is danger ofinjurin t e fibresif the temperature is too high an the extraction should therefore be regulated and controlled so as to leave theextracted chips in suitable form for the subseqent cooking operation.

During the cooking operation, the volatile constituents driven ofi from the resinous wood, for example, turpentine, etc., may be removed from the digester by bleeding, that 1s, by permitting part of the gases to escape fromthe digester. These-may be cooled and liquids recovered which are of better quality than from sulfate process operations on such woods.

Instead of cooking a single wood such as jack pine, or other pine, a mixture of resinous Woods can be cooked together, since there i is little danger of seriously over-cooking one of the woods even where a longer time is required for cooking another or'other woods which may be present in admixture. Accordingly, where various resinous woods are present in the wood pile from which the digester is charged, it is not necessary to keep the various woods separate, or to separate the segregated individual woods for separate treatment, but these woods can be used in such proportions as they may exist in the wood plle. However, where the woods which are emploged give pulp products difl'ering considera ly in their properties, it is desirable from the standpoint of uniformity of the product produced to use a particular kind of wood, or to use a uniform admixture of dif-' ferent woods containing a proximately the same proportions of the di erent woods.

In carrying out the main cooking operation, different temperatures may be employed, for example, a temperature corresponding to saturated steam at pressures up to 180 lbs. to the square inch, gauge pressure. In general, we have found it advantageous to use temperatures around 175 C. and higher for coniferous woods, for example, around 180 to 190 C.

When wood is cooked at such high temper-- atures and" pressures, the release of the pressure from c. g. 180 pounds to atmospheric involves a large heat loss due to vaporization. According to the present invention, this loss can be considerab reduced and important economies obtaine b relieving the ressure partially before blowing the charge rom the igester and using the steam so relieved in the heating of another digester charge. The steam pressure can be reduced, for example, from 180 to around 100 pounds or somewhat lower, and the steam given off may be directed into another digester which is being brought up to cooking conditions. The heat of vaporization of the steam thus released is taken advanta e of in this way and recovered in the heat1ng of another digester charge.

Instead of utilizing the-steam relieved from the digester in the manner above referred to, this steam can be relieved into an accumulator andstored under pressure, e. g., by reducing the pressure on-the digester from 180 to 100 pounds and accumulating this steam in an accumulator, and then utilizing the heat in the steam accumulator in the heating of another digester charge, for example, by forcing the steam from the accumulator into a digester charge which is being brought up to cookin conditions, or by circulating some of the coolring liquor for a fresh charge through the accumulator to condense the steam and recover the heat therein.

By proceeding in this way, the high pressure and temperature of the process can be reduced before the digester charge is blown to the blow-pit and a suflicient pressure can still be ke t on the digester to permit the blowing o the charge to the blow-pit while recovering for further use the excess heat andkpressure of the digester at the end of the coo While we have referred to the use of a cooking liquor containing only sodium sulfite, we do not exclude the presence of other chemicals, although/in general the present process does not require them. When, however, the residual liquor from the process is subjected to evaporation and carbonization, and the resulting carbonized product is leached, and is treated for the production of further amounts of normal sodium sulfite for further use in the cooking of wood, the cooking liquor thus produced may contain other compounds and particularly sodium thiosulfate or other oxysulphur compounds, and'we include the use of a cooking liquor which may contain such other compounds as within the process of the present invention. Sodium compounds such as sodium sulfate,-sodium carbonate, sodium sulfide etc., may be present in moderate amount, particularly where the cooking liquor is regenerated from the residual liquors of the process. We have produced satisfactory pulpy commercially from cooking liquors containing such other compounds, including sodium thiosul'fate, etc., and we have found that the residual liquorfrom the process can advantageously be treated for the production of further amounts of cooking liquor which may contain sodium thiosulfate or other oxysulphur compounds, as well as sodium sulfite. This process in which sodium thiosulfate etc. in addition to sodium sulfite is used in the cooking liquor forms the subject of a separate application. Serial No. 704,176, filed April 4, 1924. We consider the present process,

however, as of a broader and more generic scope, and including the use of sodium sulfite'either alone or with added amounts of other chemicals, for example, sodium thiosulfate! r We give below the operating details of certain cooks which we have made with a sodium sulfite cooking liquor on various coniferous woods. I The di ester was of the stationary vertical type, of welded steel, provided with external heat insulation. The digester was heated by the introduction of saturated steam which was received in the digester room at about 150 to 160 pounds gauge pressure. The digester was provided with both indicating and recording pressure gauges, and also with a thermometer. A steam-flow meter was used for determining the steam flow. The "digester was provided with a relief line connected to the upper portion, and steam nozzles were used in the lower portion of the digester for introducing the steam. The digester contents were blown out through a 'blow-line connected at the lower end of the digester, the stock being caught in a blow-pit, provided with perforated bottom. This blow-pit also served as a wash-pan for removal of residual liquor and washing of the stock, prior to screening it and running it over a wet machine of the usual type. I

Cook No 1: Spruce chips containing 44.5% of water were used, the actual weight of the charge of chips being 3,052 pounds, corresponding to 1,694 pounds of bone-dry wood. 750 gallons of cooking liquor were run into the digester. This liquor contained 1,350 pounds of sodium sulfite (Na SO The cover was fastened in place, and steam gradually introduced intothe digester. The

- cooking liquor as charged was at about 20 C.

The rate of steam introduction was adjusted so that at the end of one hour the gauge pressure on the digester registered 20 pounds.

[At the end of 2 hours the pressure was pounds. At the end of 3% hours the pressure was 110 pounds, and 140 pounds was reached atthe end of 3% hours. During the time taken in bringing the digester to pressure, the relief valve was occasionally opened for short intervals to permit of removing gas, steam, etc., and for promoting the circulation of the cooking liquor. After the digester had reached 140 pounds pressure in the upper portion, the pressure was maintained at or about 140 pounds for a period of five hours, except that at intervals of about one half an hour the relief valve was opened for about five minutes at a time and then closed. This opening and closing of the relief valve facilitated circulation of the cooking liquor, and such circulation was found to be advantageous in assisting in obtaining uniform treatment of the chips.

her to Cook No. 1. It contained 3,076 pounds of spruce chips, containing 1,680 pounds of bone-dry wood. The'liquor charge was 750 gallons, containing 1,350 pounds of sodium sulphite. The digester was heated in much the same manner as Cook No. 1 except that it'was held at about 150 pounds pressure for a period of four hours The pressure was reduced to 90 pounds and then the contents blown into the blow-pit. The stock was treated in a similar manner and showed 98.9% No. 1 pulp, and 1.1% of knots and screenings together.

Cook No. 3, the charge was 2,887 pounds of balsam chips containing 1,250 pounds of bone dry wood. 750 gallons of cooking liquor containing 1,350 pounds of sodium sulphite were used. The heating was substantially the same as for Cook No. 2. The product was 98.4% of No. 1 pulp and 1.6% of knots and screenings together.

Cook N o. 4 charge: Jack pine '(Pz'n'us dioarz'catd) 2,628 pounds of chips containing 1,558 pounds of bone dry wood; 660 gallons of white liquor containing 1,320 pounds of sodium sulphite, and 100 gallons of residual red liquor from a revious cook, a total of 760 gallons of 000 ing liquor being used. Three and a half hours were taken in coming to a pressure of 140 pounds. The pressure was held at about 140 pounds, gauge reading,

for a period of six hours, except for the re- -lief periods at intervals of about one half to one hour. The pressure was reduced to about 100 pounds, and then the contents) blown. The yield was 99.1% of No. 1 pulp and .9% knots and screenings together.

Cook No. 5 charge: Jack pine chips, 2,638

" pounds containing 1,594 pounds of bone-dry wood; and 750 gallons of cooking liquor containing 1,350 pounds of sodium sulphite. Three and one half hours were taken". in com- I ing up" to 140 pounds gauge pressure, and 5 held hours at about 140 pounds, except for the relief periods. The pressure was then reduced y relief to 100 ounds and the contents blown. The pro uct was 99% No. 1 pul 1% of knots and screenings.

ook No. 6 charge: J ack pine chips, 2,775 pounds, containing 1,625 pounds of bone dry wood; 550 gallonsof white liquor containing 1,072 poun s of sodium sulphite and 220 gallons of residual red liquor from a previous cook, a total of 770 gallons liquor. Three and one half hours were taken in coming up to a pressure of 140 ounds and the charge at a pressure 0 about 140 pounds for four hours,except' for the relief periods. The pressure was reduced to 100 pounds-and thecontents then blown. The product was 97.4% No. 1 pulp and 2.6% of knots and screenin s together.

In eac of the relief periods the pressure in the upper portion of the digester was reabout 8 to 10 pounds, gauge.

(look No. 7 charge: Balsam chips, 2,768 pounds, containing 1,505 pounds of bone dry wood; 400 gallons of white liquor containing 800 pounds of sodium sulphite and 350 gallons of residual red liquor from a previous cook, a total of 750 gallons of liquor. Three and one half hours were taken in coming to pressure of 140 pounds. The digester was held at about 140 pounds pressure for three and one half hours, except for the relief periods,.the pressure reduced to 105 pounds, and the contents ofthe digester blown into the blow pit as usual. The product was 96.9% No. 1 pulp and 3.1% of knots and screenings together.

Cook N o. 8 charge: Spruce chips, 3,055 pounds, containing 1,825 pounds of bone dry wood; 350 gallons of white liquor containing 700 pounds of sodium sulphite and 350 gallons of residual red liquor from a previous cook, a total of. 700 gallons of liquor. Three and one half hours were taken in coming to 140 pounds pressure, the charge was held for five hours at about 140 pounds gauge pressure, except for the usual relief periods, the pres-sure was reduced to 100 pounds pressure and the contents blown as usual. The product was 92.3% No. lp-ulp and 7.7% knots and screenings together.

Cook No. 9 charge: Balsam chips, 2,887 pounds, containing 1,250 pounds of bone dry wood, and 750 gallons of cooking liquor containing 1,950 pounds of sodium sulphite. Three and one half hours were taken in coming up to 140 pounds and the charge was held four hours at about 140 pounds, except for the relief periods, the pressure was reduced to 100 pounds and the contents blown. The product was 98.4% of N o. 1 pulp and 1.6% knots and screenings combined.

The white liquor for these cooks was made by treating a solution of sodium carbonate (probably made by the ammonia-soda process) with sulphur dioxide gas obtained from the relief er digesters after passing through a separator, operating by the so-called sulphite process. The sulphiting was continued until the solution contained a small amount of so-called free sulphur dioxide, the carbonate being entirely sulphited, then a predetermined amount of sodium carbonate was added to bring the liquors just slightly alkaline to phenolphthalein. The white liquor, therefore, consisted almost entirel of a solulion of normal sodium sulphite, NQSO free from sodium thiosulphate etc.

The cooking liquor was analyzed as follows: 10 c. c. of cooking liquor was placed in an Erlenmeyer flask, together with 20 c. c. of distilled water. The solution boiled'for three minutes, then cooled to about 20 C The cooled liquor was titrated with N/L05 by ten (10) gives the pounds of normal sodium sulphite, i. e., Na SO per U. S. gallon in the cooking liquor.

The cooks above referred to were carried out in a small commercial digester. In using larger scale commercial digesters, for-example, a digester or feet high and of 8 feet to 10 feet or so diameter, the process can be carried out in a similar way. A high content of sodium sulfite may be used, equivalent to from '60 to 80% of the bonedry weight of the wood, but a considerably. smaller amount can also be used, for example, as low as or 40% or in some cases even lower based on the bone dry weight of the wood. We do' not exclude the presence in the cooking liquor of small amounts of other chemicals. Small amounts of caustic soda may thus be present, although caustic soda in any considerable amount is not required in the process. Moderate amounts of other compounds such as sodium carbonate, sodium sulfite, sodium thiosulfate, sodium bisulfite etc., may also be present in the cooking liquor, particularly where this is regenerated from the residual li uors of the process.

Vhen a large commercial size digesier is used having a capacity, for example, of around 1,900 cubic feet and using around 7,500 gallons of cooking liquor for a digester charge, containing, for example, around 8,000 to 9,000 pounds of sodium sulfite, it is important to insure proper circulation of the cooking liquor through the charge during the cooking operation in order to secure uniform cooking results.

In such large scale digesters satisfactory circulation can be secured by providing a false bottom in the digesters and suitable piping and pumps so that the cooking liquor can be withdrawn from beneath the false bottom and circulated in copious amounts and discharged into the upper portion of the digester above the wood chips, so that the cooking liquor is quite uniformly spread out above the entire body of chips and caused to percolate in a substantially uniform manner downward through the body of chips. With liquor so circulated the liquor can be progressively heated during its passage from the bottom to the top of the digester.

While a high sodium sulfite content of the cookingliquor can be used, for example, 9,000 pounds for a digester charge of the character above mentioned, :the amount of sodium sulfite can be very much reduced from that amount. With smaller amounts of chemicals, it is advantageous and even more important to secure thorough circulation of the liquor through the digester charge. The higher the concentration of the sodium sulfite in the cooking liquor, the more active in general is the cooking operation, within reasonable limits. The higher the temperature, the more active the cooking liquor becomes. It is not advisable to cook coniferous woods at a temperature much below 175 (1., and .we prefer that the temperature be even higher than this, for exam le, up to 190 C. At temperatures much hig er than this, the digester and boiler strength required entails considerable additional expense, while if the cooking temperature be too low the time required is unnecessarily long.

The chemical pulps obtained from woods by the process of the present invention, are capable of being made into very strong papers, possessing light color even when unbleached. These pulps as a class can be bleached by the usual bleaching method. However, the pulp may advantageously be bleached by treating it after washing, preferably with hot water, with a small quantity of chlorine in the presence of water and at ordinary temperature so as to convert a substantial portion of the non-fibrous materials which generally accompany the fiber in small amount, into bleached, oxidized or chlorinated compounds, depending upon the character of the various non-fibrous constituents. These treated pulps may then be washed or otherwise treated to remove water soluble compounds and the resulting pulp then given a further treatment with a solution of bleaching powder, e. g., calcium hypochlorite. A. small amount of caustic soda may be added to the bleaching solution if desired for the purpose of increasing the amount of available alkali therein. The ulp may be bleached by subjecting it at high density, for example, from 15% to 25%, to the action of a solution of bleaching powder at atemperature around 80 to 100 F., during agitation by conveying or mixing by means of large size screw or worm conveyers. By such a bleaching and mechanical operation the pulps can be-made slower prior to their treatment in a beating engine.

Unbleached jack pine chemical pulp, projack pine pulp, then passed through two Jordan engines in series, given a light jordaning, and then fed on to a Fourdrinier type paper machine with 70 mesh wire, about 118" wide and 65 feet long, operated at 250 to 300, more or less,'feet per minute, and splendid jack pine Keebra wrapping or bag paper obtained. This, paper, when tested with a Mullen tester, showed from one to one and one half points per pound bursting strength. This was for paper which ranged from to pounds per ream of 480 sheets, each 24" x 36". This unbleached paper was very light colored, had'an excellent formation for this class of paper, and had splendid tensile strength as determined by a Schopper tensile strength tester, and also possessed cording to this invention, yield a large amount of excellent chemical pulp, the fibres of which are long, strong and fairly slender,

. and may be used for the production of someproduction of a high yield of a high grade what similar papers.

In carrying out the process of the present invention, as above pointed out, the use of a high-temperature, e. g., corresponding to 140 pounds saturated steam pressure orhigher, is advantageous in hastening the cooking op; eration and permitting this operation to be completed in a short period of time; but such a high temperature would be objectionable and would result in the-production of a considerable amount of screenings if the digester charge were heated as rapidly as possible to the cooking temperature without adequate penetration, with cooking liquor. However, by heating the digester charge gradually, over a relatively long period of time, until the preliminary impre ation and saturation of the chips witht e cooking liquor has been effected and until the'entire digester charge has been brought up uniformly to a temperature approaching the critical temperature, the cooking operation can then be carried out to completion in a relatively short period of time and with the pulp, without material loss of the wood in the form of screenings, and also without the use of caustic soda etc. in the cookingliquor, although caustic'soda etc.---Iieed not be entirely excluded from the cooking liquor..

The use of a high temperature, around 140 lbs. steam pressure, would tend, in a process such as the soda process, to cause destruction or over-cooking of a considerable part of the digester charge but with the process of the present-invention, the charge can safely be heated during the cooking operation to such a high temperature without objectionable destruction of the charge, and.

such high temperatures are moreoveradvanta-geous in enabling the cooking operation to be completed in a relatively short time, thus increasing the production capacity of the digester, and making up for the relatively prolonged period used in bringing the digester charge up to the cooking temperature.

When the cookin operation is completed, the pressure may fie partly reduced, e. down to 50 or pounds,'more or less, Ey withdrawing vapors, e. g., steam, etc, from the top of the digester, and the digester charge can then be blown from the digester into the blow-pit by the remaining pressure. A partial reduction of the pressure in this way enables a considerable part of the heat contained in the charge to be recovered from the vapors withdrawn during the partial reduction in pressure. This heat ma be stored in an accumulato1 and thus a vantageouslymade available in a further cook.

The residual liquor produced by the cooking operation will contain considerable .amounts of resinous constituents or reaction productsthereof such as resinate, particularly Where highly resinous woods are cooked; Such residual liquors may be treated for the production of further amounts of cooking liquor therefrom. vA part of the residual liquor can be used over again to advantage as part of the make-up liquor for a subse 'quent cook, as it generally contains some active chemicals, or this liquor can be first partially purified and then used over again in this way. For example,- the residual liquor may be treated with sulfur diox'ide and acidified. to precipitate part of the organic matter and to decompose some of the resinates, and the precipitated and separated matter may then be promptly removed to avoid resolution and the liquor then neutralized with sodium carbonate before using the liquor or part of it over again in subsequent cooks.

We claim:

coniferous woods which comprises treating the wood with a liquor containin essentially 1. The. method of producing pulp from a normal sulfite of an alkali to e ect impregnation of the wood with the liquor before reaching the active cooking temperature, and 5 thereafter continuing the pulp-making operation, the amount of sul-fite in the cooking; liquor belng sufficient to maintain the liquor alkaline tion.

to litmus during thecooking opera- 2. The method of producing pulp from coniferous wood which comprises subjecting the same to impregnation with a cooking liquor containing essentially a normal sulfite of an alkali, and subsequently subjecting the same to a cooking operation under pressure and at an elevated temperature, the amount of sulfite in the cooking liquor being suficient to maintain the liquor alkaline to litmus during the cooking operation.

3.'The method of producing pulp from resinous wood which comprises subjecting the same to a cooking operation under pressure and at an elevated temperature with a cooking liquor containing essentially a normal sulfite of an alkali, in amount suflicient to maintain the liquor alkaline to litmus during the cooking operation, the liquor being circulated through the digester charge.

4. The method of producing pulp from resinous wood, which comprises subjecting the same to a cooking operationunder pressure and at an elevated temperature with a cooking liquor containing essentially a normal sulfite of an alkali in amount sufiicient to maintain the liquor alkaline to litmus during the cooking operation, the cooking operation being carried outin a digester under substantially uniform temperature conditions.

5. The method of producing pulp from coniferous wood-which comprises charging the digester with the wood chips and with a cooking liquor containing essentially a normal sulfite of an alkali in amount suflicient to maintain the liquor alkaline to litmus during the cooking 'operation, gradually heating the charge to secure impregnation of the chips with the cooking liquor before the charge reaches the cooking temperature and then carrying out the main cooking operation at a high temperature and pressure.

6. The method of producing pulp from pine-which comprises subjecting pine chips to preliminary impregnation with a cooking liquor containing essentially a normal sulfite of an alkali at a temperature below that of the cooking operation and subsequently cooking the pine wood at a hi h temperature and pressure, the amount 0 sulfite. in the cooking liquor being sufiicient to maintain the liquor alkaline to litmus during the cookin operation. I

The method of producing pulp from pine which comprises charging the digester with the pine chips and with a cooking li uor containing essentially a normal sulfite 0 an alkali in amountsufiicient to maintain the liquor alkaline to litmus during the cooking operation, gradually heatingv the same to secure impregnation of the chips with the cooking liquor before the charge reaches the cooking temperature and then carrying out the main cooking operation at a high temperature and pressure in excess of about 17 0 C.

8. The method of producing pulp from coniferous wood which comprises charging the digester with wood chips and with a cooking liquor containing essentially a normal sulfite of an alkali in amount suflicient to maintain the liquor alkaline to litmus during the cooking operation, withdrawing the cooking liquor from the lower portion of the digester, re-introducing the cooking liquor into the upper portion of the digester, and

heating the circulating liquor between the points of withdrawal and of re-introduction.

9. The method of producing pulp from coniferous wood which comprlses charging the digester with the wood chips and with the cooking liquor containing essentially a coniferous wood which comprises subjecting the same to a cooking operation under pressure and at an elevated temperature with a cooking liquor containing essentially a normal sulfite of an alkali, said cooking liquor also containing residual liquor from the process, and the digester charge being subjected to impregnation with the cooking liquor and being thereafter subjected to the main cooking operation, the amount of sulfite in the cooking liquor being sufficient to maintain the liquor alkalineto litmus duringthe cooking operation.

11. The method of producing pulp from resinous wood which comprises gradually heating a digester charge of the wood to the cooking temperature with a cooking liquor containing essentially a normal sulfite of an alkali to effect impregnation of thewood with the cooking liquor and thereafter continuing the cooking operation, the amount of used alkali sulfite being at least 35 per cent by weight of the bone dry weight of the wood treated.

12. The method of producing pulp from resinous wood which comprises subjecting the same to a cooking operation with a cooking liquor containing essentially a normal sulfite of an alkali, the cooking operation being carried out in two successive stages, of which the first is apreliminary impregnation stage and the second is the main cooking stage carried out at a higher and active cooking temperature, and the amount of sulfite in the cooking liquor being suflicient to maintain the liquor alkaline to. litmus during the cooking operation. v

13. The method of producing pulp'from resinous wood which comprises subjecting operation and subr- .quently cooking the wood I chips at a temperature corresponding toa saturated steam pressure of about to pounds per square inch.

14. The method of producing pulp from coniferous wood which comprises charging the digester with the wood chips and with/a liquor containing essentially a normal sulfite of an alkali in amount suflicient to maintain the liquor alkaline to litmus during the cooking operation, gradually heating the charge to secure impregnation of the chips with the liquor, and then carrying out the main cooking operation at a high temperature and pressure of about 140 pounds saturated steam pressure or higher, vapors being relieved from the digester durin thecooking operation,

15. The metho of producing pulp from coniferous wood which comprises subjecting the wood to'a preliminary impregnation with a cooking liquor-con aining essentially a normalsulfite of an alkali, the amount of such liquor being sufiicient to submerge the entire charge of wood chips, and subsequently cooking the wood chips at a high temperature "and pressure with a reduced amount of cooking liquor which is circulated through the charge,

the amount of sulfite in thecooking liquor being suflicient to maintain the liquor alkaline to litmus during the cooking operation.

16. The method of producing pulp from coniferous wood which comprises subjecting the wood to a preliminary impregnation with a relatively concentrated solution of a normal sulfite of an alkali andthereby absorbing in the wood chips an amount'of a sulfite of an alkali sufiicient to maintain the chips substantially neutral or alkaline to litmus during the subse uent cooking operation and subsequent- 1y coo ing the wood chips at a high temperature and pressure.

17. The method of producing pulp from coniferous wood which comprises subjecting the wood to a partial vacuum, applying to the evacuated wood a cooking liquor containing essentially a normal sulfite of an alkali and subsequently subjecting thewood to a cooking operation at a high temperature and pres-. sure with such a cooking liquor, the amount of sulfite in the cooking liquor being sufiicient to' maintain the liquor alkaline to litmus duri ing the cooking operation.

18. The method of producing pulp from resinous wood which comprises charging a digester with wood chips and with a cooking liquor containing essentially a normal sulfite of an alkali in amount suflicient to maintain the liquor alkaline to litmus during the cooking operation, heating the digester charge to effect impregnation of the chips with theliquor and subsequently carrying out a cooking operation at a temperature above 170 (3. 19. The method of producing pulp from resinous wood which comprises charging a digester with wood chips and with a -cooking liquor containing essentially a" normal sulfite of an alkali in amount suficient to maintain the liquor alkaline to litmus during the cookto 190 C. j

20. The method of producing pulp from pine which com rises charging the digester with the pine chips and with a cooking 1i uor containing essentially a normal sulfite 0 an alkali-in amount suflicient to maintain the liquor alkaline tolitmus during the. cooking 0 eration, gradually heating the digester paper obtained from chemical pulp from.

coniferous wood by cooking the wood with a cookin liquor which contains a normal sulfite 0 an alkali in amount sufiicient to maintain the liquor alkaline to litmus, said paper having a bursting strength in excess of a'point per pound.

' As a new product, a market paper comprlslng fibrous material obtained by cooking coniferous wood with a cookingliquor which contains essentially a normal sulfite-of an alkali in amount suflicient to maintain the ,liquor alkaline to litmus, the paper being characterized by relatively light color and having a bursting strength equal to at least nine tenths of a point per pound, when tested with a Mullen tester. I

24. The method of producing naval stores and chemicalpulp from resinouswoods which comprises extracting resinous constituents from the wood at a temperature below about 100 C. and subjecting the extracted wood to a cooking operation with a cooking liquor containing essentially a normal alkali sulfite in amount suflicient to maintain the cooking liquor alkaline to litmus.

25. In a cooking of wood chips-with a cooking liquor which contains essentially a normal sulfite of an alkali in amount sufficient to maintain the cooking liquor alkaline to litmus, at steam pressures of at least 100 pounds per square inch, the relieving of steam from the digester and the utilization of such relieved steam in the heating of another digester charge.

26. In the cooking of coniferous wood' chips. with a cooking liquor which contains essentially a normal sulfite of an alkali in amount suficient to maintain the cooking liquor alkaline to litmus, at steam pressures of at least 100 pounds per square inch, the

relieving of steam from the digester into an accumulator until the pressure within the digester is below 100 pounds per squareinch g operation at a temperature around 180- prior to blowing the digester charge, and

utilizing the heat in the steam accumulator charge, and utilizing the heat contained therein for the heating of another digester charge.

28. In the cooking of resinous woods with a cooking liquor which contains essentially a normal sulfite of an alkali in amount sufficient to maintain the cooking liquor alkaline to litmus, the relieving of vapors from the digester and condensation of vapors and the recovery of the liquids thus obtained.

29. In theart of obtaining bleached chemical pulp from pine wood, the steps which comprise cooking pine wood with a cooking liquor which contains essentially a normal alkali sulfite in amount sufficient tomaintain the cooking liquor alkaline to litmus, blowing the digester charge, separating fibrous material from the residual liquor, washing the fibrous material, screening the fibrous material, treating the screened chemical pulp in the presence of water with a regulated amount of chlorine, removing water soluble products from the treated chemical pulp, and thereafter subjecting the treated chemical pulp to a bleaching operation, followed by washing of the bleached chemical pulp.

30. As a new product, paper which comprises the bleached chemical pulp of the preceding claim.

31. The treatment of residual liquors resulting from the cooking of coniferous woods with a cooking liquor which contains essentially a normal sulfite of an alkali in amount suflicient to maintain the cooking liquor alkaline to litmus, which comprises treating the residual liquor with sulphur dioxide or an acid sulfite, promptly separating precipitated organic matter, and using the liquor for the production of cooking liquor for the process.

32. The methood of producingpulp from coniferous wood, which comprises impregnating the wood chips withcooking liquor,

' containing a normal sulfite of analkali metal as its predominating reagent, in suflicient amount, prior to reaching the active cooking temperature, to prevent subsequent objectionable alteration of non-fibrous material of the wood, and continuing the treatment of the chips with such cooking liquor at an elevated temperature until substantially all of the wood fibers are rendered readily separable.

33. The method of producing pulp from coniferous wood, which comprises hharging the wood chips and a monosulfite of an alkali metal cooking liquor into a digester, circulating the cooking liquor and gradually heating it under such conditions as to impregnate the wood'chips, prior to reaching the active cooking temperature, with an amount of alkali metal sulfite in solution suflicient to pre vent objectionable alteration of non-fibrous material of the Wood during the further treatment, and continuing to treat the chips with such cooking liquor at an elevated temperature until substantially all of the wood fibers are rendered readily separable.

34. The method of producing pulp, which comprises slowly raising the temperature of a mixture of coniferous wood chips and cooking liquor containing alkali metal sulfite so as to impregnate the chips with alkali metal sulfite in solution to such extent as" to substantially prevent undesirable alteration of non-fibrous material of the chips during the subsequent treatment and thereafter continuing the treatment of the chips with such cooking liquor at an elevated temperature until substantially all of the wood fibers are rendered readily separable, the amount of alkali metal sulfite being sufficient to maintain the cooking liquor alkaline to litmus until the end of the cooking operation.

35. The method of producing wood pulp from resinous wood, which comprises digesting the wood with a liquor containing soluble monosulfite as substantially the only digesting reagent, the quantity of monosulfite used being sufiicient to continue the cook and the cook being continued until the encrusting materials have been dissolved and disintegrated and resinous constituents have been dissolved and separable wood fibres characterized by extraordinary strength, flexibility, matting and bleaching qualities have grated and resinous constituents have been dissolved and separable wood fibres characterized by extraordinary strength, flexibility, matting and bleaching qualities have been produced, substantially as described.

In testimony whereof we affix our signatures.

LINN- BRADLEY. EDWARD P. MoKEEFE. 

